NC0026441_Wasteload Allocation_19910228

NPDES DOCUMENT SCANNIM& COVER SHEET
NPDES Permit: NCO026441
Siler City WWTP
Document Type: Permit Issuance
Wasteload Allocation
Authorization to Construct (AtC)
Permit Modification
Engineering Alternatives Analysis
201 Facilities Plan
Instream Assessment
Correspondence re:
Permit History Date Range:
Document Date: February 28, 1991
THIS DOCUMENT IS PRIMTED ON REUSE PAPER - ISMORE ANY CONTEMT ON THE
REVERSE SIDE

j
n
Q
r4 ti cif
a � o i w b "3
y OO b
O' o
4
C d
o
U
O
Q ' U LAJ N 4al
i I �
tw�y
a
U
0
0O O
bA C
W
z GO
C4
a w
O
Q
N
1� N p o a— ►n � N o ,� c
in
vn
O '
' d
c
CD
Q cn O c o
r"
- O
W U W
CA
03
►u
3
Cd
o
ti
O T
' o a
� 3
Ln
� a �
4
C d
o
U
O
Q ' U LAJ N 4al
i I �
tw�y
a
U
0
0O O
bA C
W
z GO
C4
a w
O
Q
N
1� N p o a— ►n � N o ,� c
in
vn
O '
' d
c
CD
Q cn O c o
r"
- O
W U W
CA
03
►u
3
Cd
o
ti
O T
' o a
� 3
Ln
� a �
W
z GO
C4
a w
O
Q
N
1� N p o a— ►n � N o ,� c
in
vn
O '
' d
c
CD
Q cn O c o
r"
- O
W U W
CA
03
►u
3
Cd
o
ti
O T
' o a
� 3
Ln
� a �
CA
03
►u
3
Cd
o
ti
O T
' o a
� 3
Ln
� a �

2/11/91 -1- Request No. %O AA
Facility Name:
NPDES No.:
Type of Waste:
Facility Status:
Permit Status:
Receiving Stream:
Stream Classification:
Subbasin:
County:
Regional Office:
Requestor:
Date of Request:
Topo Quad:
FACT SHEET FOR WASTELOAD ALLOCATIONS
Town of Siler City WWTP
NCO026441
70% Domestic, 30% Industrial
Existing
Modification
Loves Creek
C
030612
FEB 181991
DEB %6 moi
Chatham Stream Characteristic:
Raleigh USGS #
02.1 17.51150 prf?rqIT
rt,rA!r
Drainage Area:
7.9 sq. mh.
E21NW Summer 7Q10:
0.25 cfs
Winter 7Q10:
0.40 cfs
Average Flow:
8.70 cfs
30Q2:
Wasteload Allocation Summary
Siler City originally requested an expansion from 1.8 MGD to 4.0 MGD in 1988. Permit was
never issued due to public opposition and EIS/201 Facilities Plan requirements. The previous WLA was
based on a Level-B modeling analysis, which was found to be inadequate for an application to the Rocky
River. Based on a Level-C modeling analysis, new water quality data and biological data, and the latest
pretreatment information, the following limits and requirements apply for a 4.0 MGD discharge by the
Siler City WWTP. See attached documentation for more information.
(approach taken, correspondence with region, EPA, etc.)
WASTELOAD SENT TO EPA?(Major) _ (Y or N)
(if yes, then attach schematic, toxics spreadsheet, copy of model, or if not modeled, then old assumptions
that were made, and description of how fits into basinwide plan)
Recommended by: Ai �- J a WW Dater
Reviewed by (` �
Instream Assessment: 2A,� /� l_. /i _ L.lIdXleajl Date: to P
Regional Supervisor:
Permits &
RETURN TO TECHNICAL SERVICES BY
—� Date: Z(�
MAR 15 1991
C' .B f�"' e t 0�-- 'ate- x.-

2/11/91 -2- Request No.
Existing Limits:
Wasteflow (MGD):
BOD5 (mg/1):
NH3N (mg/1):
DO (mg/1):
TSS (mg/1):
Fecal Coliform (/100 ml):
pH (Si):
Oil & Grease (mg/1):
TP (mg/1):
TN (mg/1):
Residual Chlorine
Recommended Limits:
Wasteflow (MGD):
BOD5 (mg/1):
NH3N (mg/l):
DO (mg/1):
TSS (mg/1):
Fecal Coliform (/100 ml):
pH (Sin:
Oil & Grease (mg/1):
MBAS (mg/1):
TP (mg/1):
TN (mg/1):
Residual Chlorine (ug/1):
Limits Changes Due To:
Instream Data
Ammonia Toxicity
Chlorine
Nutrient Sensitive Waters
HQW
New 7Q10 flow data
Special Modeling Studies
New facility information
CONVENTIONAL PARAMETERS
Monthly Average
Summer Winter
1.8
1.8
15
30
10
NR
5
5
30
30
1000
1000
6-9
6-9
Monitor
Monitor
Monitor
Monitor
Monitor
Monitor
Monitor
Monitor
Summer Winter
4.0
4.0
5
10
1
2
6
6
30
30
200
200
6-9
6-9
30
30
0.5
0.5
0.5
Monitor
Monitor
Monitor
17
17
Parameter(s) Affected
BOD5, DO, NH3-N, -fP
NH3-N
Chlorine
BOD5, DO, NH3-N, TP
Toxics, Oil&Grease, MBAS
Other: (explanation of any modifications to past modeling analysis including new flows, rates, field
data, interacting discharges, etc.) (See page 4 for Miscellaneous and special conditions if apply)
- Chlorine limit not required if aitenate method of disinfection is utilized by the expanded plant.
- TP limit applies from May through September only.

2/11/91 -3- Request No.
TOXICS
Toxicty Limit Monitorin , Schedule
Existing Limit: Chronic/Ceriodaphnia/Qrtrly 91% IWC Mar, Jun, Sept, Dec
Recommended Limit: Chronic/Ceriodaphnia/Qrtrly 96% IWC Mar, Jun, Sept, Dec
Toxics or metals limits
Existing Limits: Daily Maximum
Cadmium (ug/1):
Chromium (ug/1):
Copper (ug/1):
Nickel (ug/1):
Lead (ug/1):
Zinc (ug/1):
Cyanide (ug/1):
Phenols (ug/1):
Mercury (ug/1):
Silver (ug/1):
Recommended Limits:
Daily Maximum
Cadmium (ug/1):
Chromium (ug/1):
52
Copper (ug/1):
Monitor
Nickel (ug/1):
Monitor
Lead (ug/1):
26
Zinc (ug/1):
Monitor
Cyanide (ug/1):
5.2
Phenols (ug/1):
Mercury (ug/1):
0.012
Silver (ug/1):
Monitor
Aluminum (ug/1):
Monitor
Limits Changes Due To:
Change in 7Q10 data
Change in stream classification
Relocation of discharge
Change in wasteflow
New pretreatment information
Failing toxicity test
Other: (onsite toxicity study, interaction, etc.)
Parameter(s) Affected
All
All

Facility Name , Idv/A Sc l2 r _C' u WWI? Permit # Cf1 ZL t{�
CHRONIC TOXICITY TESTING REQUIREMENT (QRTRLY)
The effluent discharge shall at no time exhibit chronic toxicity in any two consecutive toxicity tests,
using test procedures outlined in:
1.) The North Carolina Ceriodaphnia chronic effluent bioassay procedure (North Carolina Chronic
Bioassay Procedure - Revised *June 1988) or subsequent versions.
The effluent concentration aLwhich there may be no observable inhibition of reproduction or
significant mortality is -L-% (defined as treatment two in the North Carolina procedure
document). The permit holder shall perform quarterv monitoring using this procedure to establish
compliance with the permit condition. The first test will be performed after thirty days from
issuance of this permit dw-ing the months of date Juei. S5� , Kc _ .. Effluent
sampling for this testing shall be performed at the NPDES permitted final effluent discharge below
all treatment processes.
All toxicity testing results required as part of this permit condition will be entered on the Effluent
Discharge Monitoring Form (MR-1) for the month in which it was performed, using the parameter
code TGP3B. Additionally, DEM Form AT-1 (original) is to be sent to the following address:
Attention: Environmental Sciences Branch
North Carolina Division of
Environmental Management
P.O. Box 27687
Raleigh, N.C. 27611
Test data shall be complete and accurate and include all supporting chemical/physical measurements
performed in association with the toxicity tests, as well as all dose/response data. Total residual
chlorine of the effluent toxicity sample must be measured and reported if chlorine is employed for
disinfection of the waste stream.
Should any single quarterly monitoring indicate a failure to meet specified limits, then monthly
monitoring will begin immediately until such time that a single test is passed. Upon passing, this
monthly test requirement will revert to quarterly in the months specified above.
Should any test data from this monitoring requirement or tests performed by the North Carolina
Division of Environmental Management indicate potential impacts to the receiving stream, this
permit may be re -opened and modified to include alternate monitoring requirements or limits.
NOTE: Failure to achieve test conditions as specified in the cited document, such as MiniMUM
control organism survival and appropriate environmental controls, shall constitute an invalid test
and will require immediate retesting(within 30 days of initial monitoring event). Failure to submit
suitable test results will constitute noncompliance with monitoring requirements.
7Q10 0,15 cfs
Permited Flow N.0 MGD
IWC% V %4
Basin & Sub -basin 630612
Receiving Stream -Loves Ctek
County Chaff AJI
Recommended by:
")- J-
Date 2(111,1!
*Chronic Toxicity (Ceriodaphnia) P/F at%,MO. Tun , See Part, Condition �.

-4-
Request No.
MISCELLANEOUS INFORMATION & SPECIAL CONDITIONS
Miscellaneous information pertinent to the renewal or new permit for this discharge. Include relationship
to the Basinwide management plan:
Facility has severe I&I problems. The lower Rocky River provides habitat for the federally
endangered Cape Fear Shiner. Mussel surveys reveal substantial degradation of stream quality below the
discharge.
INSTREAM MONITORING REQUIREMENTS:
Upstream: Y Location: 1) Loves Creek at the Plant Entrance
2) Rocky River at the Highway 64 bridge
Donwstream: Y Location: 1) 200 feet downstream of the confluence of Loves Creek
and the Rocky River
2) At SR 2170
Special Instream monitoring locations or monitoring frequencies:
Monitor for temperature, DO, fecal coliform, and conductivity.
From May through September, additional monitoring of TP, PO4, NH3-N, and NOx, should be
required.
SPECIAL INSTRUCTIONS OR CONDITIONS
SCHEDULE REQUIREMENTS:
rM Ca^�^ ra.0
a/fwn 5, �•
/jj! Ltd��77vr o/
(for P&E or region to recommend time frame for implementing new limits)
ADDITIONAL 'REVIEWER" COMMENTS:
Additional Information attached? (yes or no) If yes, explain attachments.
Memos of explanation.

—D Q-
Division of Environmental Management
Memorandum
To: Arthur Mouberry
From: Mike Scoville MOS
November 9, 1990
Nov
Thru: Ruth Swanek VC5 ?�
Trevor Clements
PER,'�iI1S & ENGiKERING
i
Subject: Instream Assessment for the Town of. Siler City WWTP
(NPDES No. NC0026441, Chatham County)
SOC EMC WQ No. 90-05
Summary
JEC
The Town of Siler City WWTP discharges to Loves Creek approximately 0.4 miles
above it's confluence with the Rocky River in Chatham County. The WWTP has been out
of compliance with it's NPDES permit limits for flow, BOD5, NH3-N, and TSS, largely
due to excessive infiltration and inflow (I&I) that flood the plant after heavy rains. The
Town has recently been the center of some controversy by requesting a permit
modification allowing the expansion of the WWTP to a 4.0 MGD design capacity, up from
1.8 MGD. The expansion is not only to accommodate future wastewater, but also to treat
the the surges of I&I more effectively and to eliminate the occurrences of bypasses that
result from the plants inability to handle it. Due to the sensitivity of the Rocky River,
the low DO concentrations already observed in the receiving waters, and the threat to
wildlife downstream, the expansion to 4.0 MGD would require very stringent effluent
limits (see attached).
The current SOC request is for an additional 0.10752 MGD of flow and relaxed
effluent limits for BOD5, NH3-N, and TSS. The flow balance is not entirely accurate
because the existing 1.8 MGD design flow is often exceeded by I&I in such amounts that a
0.10752 MGD increase is insignificant. However, during dry events, when the
streamflow is low and the effluent has the greatest impact, I&I is at a minimum and the
proposed SOC flow can be modeled accurately to evaluate it's impact. At the proposed
limits, although_the EMC criteria are not violated by the additional flow, the expected
impacts on water quality are so severe that, in light of the observed DO concentrations
downstream and the urgent need for improvement of the Siler City WWTP, Technical
Support does not recommend that the additional flow be approved.
Analysis and Discussion
The instream analysis for Siler City's proposed SOC was performed using the
same QUAL2E model used for the wasteload allocation for the proposed plant expansion. A
summary of that analysis is attached. The model was modified to reflect the proposed SOC
effluent limits and run at the average flow from August 1989 to July 1990 (1.6621
MGD) and at the increased SOC flow (1.80052 MGD). The upstream water quality
characteristics, derived from instream monitoring data, were not changed.
,40

Figure 1. Rocky River Predicted DO Profiles; SOC Instream Assessment
c
0
X
O
C)
O
7
6
5
4
3
2
1
0
0
5 10 15 20
Mile
Table 1.
QUAL2 Model Input for Siler City WWTP
Instream Assessment
• Upstream
Effluent
Characteristics
Parameter
Loves Creek
Rocky River
Average Flow
8/89 - 7/90
Proposed
1 SOC Flow
Existing
Limits`
Flow
0.2 cfs 0.3 cfs
1.6621 MGD
1.8005 MGD
1.80 MGD
BOD5
mg/1
1.670 2.130
35.0
35.0
15.00
DO
mg/1
4.410 2.700
5.0
5.0
5.00
Organic N
mg/1
0.600 0.650
6.92
6.92
5.00
NH3-N
mg/l
0.325 0.575
20.0**
20.0**
10.00
NOx
mg/1
1 0.640 0.517
1 0.65
0.65
0.65
Not modeled.
Default Values for modeling purposes. Proposed SOC has no ammonia limit.
4.
L G. U,

Division of Environmental Management
November 5, 1990
Mem mndum
To:
Arthur Mouberry
Alan Clark
Steve Tedder
Don Safrit
Bobby Blowe
Thru:
Trevor Clements
Ruth Swanek
From:
Mike Scoville
Subject:,
Town of Siler City WLA Modeling Analysis (NPDES No. NC0026441, Chatham
County)
Summary
In 1988 the Town of Siler City requested an expansion for its wastewater treatment plant to a
wasteflow of 4.0 MGD from 1.8 MGD. At that time, a Level-B modeling analysis was performed and permit
limits recommended. Since then, a Level-C analysis was required to verify the limits necessary to protect
North Carolina's instream standards at an expanded wasteflow, due to public interest in the issue, the
inadequacies of the Level-B model application to the Rocky River, requirements of the EIS process, and
WWTP design considerations. The entire wasteload allocation analysis was re -initiated, and based on available
information and data, the following limits should apply if an NPDES permit is issued for Siler City with a
design flow of 4.0 MGD:
Summer
Winter
Flow
MGD
4
4
BODS
mg/l
5
10
NH3-N
mg/1
1
2
DO
mg/1
6
6
TS S
mg/1
30
30
Fecal Coliform
#/100 ml
200
200
pH
SU
6-9
6-9
Oil & Grease
mg/1
30
30
MBAS
mg/l
0.5
0.5
Lead
ug/l
26
26
Chromium
ug/l
52
52
Cyanide
ug/l
5.2
5.2
Mercury
ug/l
0.012
0.012
Copper
ug/l
Monitor
Monitor
Nickel
ug/l
Monitor
Monitor
Zinc
ug/1
Monitor
Monitor
Silver
ug/I
Monitor
Monitor
Aluminum
ug/l
Monitor
Monitor
Total Residual Chlorine'
ug/l
17
17
Total Phosphorus
mg/l
0.5*`
NR
Chronic/Ceriodaphnia/Quarterly whole effluent toxicity test at 96% IWC
Not necessary if an alternate method of disinfection is utilized
" Total Phosphorus Limit required May through September only.
The recommended limits are necessarily stringent to meet water quality criteria downstream of the
discharge. Downstream data and the modeling analysis have demonstrated that the existing secondary permit
limits are not adequate to protect downstream DO. In fact, the existing 1.8 MGD wasteflow, when modeled at

limits more stringent than those existing (see below), was not expected to protect the North Carolina instream
DO concentration. In addition to the above limits applying to the proposed 4.0 MGD, the Town should be
informed that Technical Support will recommend a revision in existing effluent limits for their current design
flow as necessary to protect the downstream DO concentrations. Therefore, whether the expansion is approved
or not, modification of the plant will be required. Revised limits for the 1..8 MGD would be very similar to
those listed above.
Modeling f Oxygen Conswming Wastes
A modeling analysis of Loves Creek and the Rocky River below the Siler City WWTP discharge was
recently completed to evaluate the impact of the effluent on instream dissolved oxygen concentrations and to
determine the NPDES limits necessary to protect NC water quality standards at a wasteflow of 4.0 MGD. A
QUAL2E water quality model was developed for approximately 21 miles of stream below the plant. Hydraulic
functions for the model were developed based on the results of a low flow time of travel study performed by
Black & Veatch this past August and September. Rates and kinetics were estimated based on best professional
judgement and on typical values observed in similar streams. The upstream characteristics of Loves Creek and
Rocky River, averaged from Siler City's instream monitoring data, were kept the same for each simulation, so
any change in the model results are directly attributable to the effluent characteristics. Four scenarios were
simulated:
1. Average conditions from August 1990
2. Current permit limits for 1.8 MGD
3. Proposed permit limits for 4.0 MGD
4. No discharge
The model inputs for the upstream and various effluent conditions are shown in Table 1. While not a
formally calibrated model, the DO profile predicted by the model for average low flow conditions provides a
close fit to instream DO data collected on several separate occasions during warm, low flow conditions of 1989
and 1990. This is shown in Figure 1. Most importantly, the predicted DO profile accurately matches the
observed DO in the impact and recovery zone; the model is appropriate for evaluating the impacts of the
wastewater on the water quality in this area. It is important to remember that the model simulation represents
mean conditions, while the data points in Figure 1 are instantaneous samples.
Table 1.
QUAL2 Model Input for Siler City WWTP
Upstream
Effluent Characteristics
Loves Creek
Rocky River
8/90 Average
xisting Flow
Proposed
Parameter
rInt.Limits*
Expansion
Flow
0.2 cfs
0.3 cfs77
- 1.63 MGD
1.80 MGD
4.0 MGD
BOD5
mg/1
1.670
2.130
5.33
12.00
5.00
DO
m g/I
4.410
2.700
6.10
6.00
6.00
Organic N
mg/1
0.600
0.650
6.92
5.00
5.00
N113-N
mg/1
0.325
0.575
6.90
2.00
1.00
NOx
mg/1
0.640
0.517
0.65
0.65
0.65
* Intermediate Limits, between secondary and tertiary treatment.
Low flow conditions are frequently experienced in the Rocky River, often for extended periods of
time. This is due to the presence of a reservoir upstream that releases little or no water to provide assimilative
capacity. As a result, 7Q10 conditions are experienced much more often than every ten years, and DO
violations probably occur every summer. The lack of significant instream flow facilitates low velocities and
substandard DO concentrations. Non -point loading also affects the water quality to some extent, particularly in
Loves Creek above the Siler City WWTP. Since the flow characteristics of the Rocky River also lead to
extended periods of time that the stream is dominated by the effluent, a very high quality of effluent is
necessary to protect the water quality standards.

Figure 2 shows the predicted DO profiles for each of the four scenarios previously mentioned. As can
be seen, the discharge has a significant impact on the water quality for approximately five stream miles
immediately below the plant. The average existing conditions produce the most severe DO sag, although
substandard DO concentrations are predicted in each of the models in which the discharge was included. The
Figure 1. Observed Instream DO Concentrations and Predicted DO Profile.
10 T
Ca6
5
O
A 4
2
CI;
0 5 10 15 20
►F KM
model simulation with no discharge should be interpreted with caution, however, due to the uncertainty of how
the stream would behave with so little flow. The DO profile for the most part reflects only changes in
hydraulics; the oxygen -consuming parameters are absent for most of the model because of the slow velocity.
In reality some sort of equilibrium would most likely be reached. The no -discharge model provides a good
indication of water quality in the upper part of the model, though, and it's results were included in Figure 2 for
comparison. In every case that was modeled, the Rocky River seemed to recover by approximately the fifth
mile, below which the effluent characteristics are expected to have little effect on instream DO.
Limits representative of advanced secondary treatment (between the existing and proposed limits) were
modeled at a flow of 1.8 MGD, rather than 4.0 MGD. As can be seen in Figure 2, under this scenario
substandard DO concentrations would be expected for an extended stretch of the stream. The results of other
model runs (not shown) indicate the even lower DO concentrations would result from a 1.8 MGD discharge
with secondary treatment and from a 4.0 MGD discharge with the existing limits. The predicted DO profile
shown is included for comparison of the range of limits necessary for the maintainence of the DO stream
standard. In other words, the lower flow with the better treatment has less impact than either of the existing
permits, and it is still unacceptable from a DO standpoint.
The Rocky River model is sensitive to organic nitrogen and ammonia nitrogen loading from the WWTP. For
example, although the average effluent BOD5 was less than half of the permitted amount, the DO sag was
more severe due to excessive levels of organic and ammonia nitrogen (see Table 1). In the allocation model
runs, the amount of organic nitrogen in the effluent was a critical factor in the DO sag. For the average
effluent concentration, a value of 6.92 was estimated based upon effluent values of total nitrogen and ammonia
nitrogen. For the two allocation scenarios a conservative value of 5 mg/I was assumed. Generally, as the
removal of ammonia increases, the effluent organic nitrogen should decrease as well. Based on other facilities'
effluent data, if Siler City were meeting an NH3-N limit of 1 mg/l, their organic nitrogen would be
considerably less, probably around 2-3 mg/I. The sensitivity of the model to organic nitrogen was tested in

I
allocation runs for the proposed expansion by modeling effluent concentrations of 1, 5 and 10 mg/l. The
predicted DO profiles resulting from this analysis are shown in Figure 3. It is evident that based on the model
results, if the other oxygen -consuming limits were met, organic nitrogen could potentially make the difference
of whether the instream DO standard is maintained. If the Siler City WWTP were to maintain a high
7
6
5
4
Q 3
2
1
0
0
Figure 2. Rocky River Predicted DO Profiles
5 10 15 20
Mile
Figure 3. Sensitivity of Siler City WWTP Allocation Model to Organic Nitrogen
(Values are effluent organic nitrogen)
a
7
6
5
4
3
2
1
0
0
5 10 15 20
Mile

degree of nitrogen removal and consistently meet the proposed limits, the DO stream standard would not be
expected to be violated. This modeling analysis confirms that the limits derived in the 1988 Level-B WLA
would not adequately protect water quality in Loves Creek and the Rocky River.
Nutrients
A total phosphorus limit was recommended to prevent over -enrichment of the natural stream system
per 15A NCAC 2B .0211 (b)(3)(A), which states "the Commission or its designee may prohibit or limit any
discharge of waste into surface waters if, in the opinion of the Director, the surface waters experience or the
discharge would result in growths of microscopic or macroscopic vegetation such that the standards established
pursuant to this Rule would be violated or the intended best usage of the waters would be impaired." Due to
the significance of Siler City's discharge on the downstream TP concentrations during low flow periods, and
based on staff observations and citizen complaints of algal growth on the substrate and the water surface, a TP
limit is appropriate. The above regulation specifically applies to slow moving waters not designated as trout
waters.
T xic
The toxics limits were all determined according to standard Division procedure. A mass balance was
performed for each individual parameter and a limit derived which represents the maximum daily allowable
effluent concentration that will protect the instream standard. The mass balance used the plant design flow (4.0
MGD) and the 7Q10 of Loves Creek at the point of discharge (0.25 efs). Monitoring requirements for metals
were based on the latest pretreatment headworks analysis and priority headworks analysis.
The total residual chlorine limit is to prevent toxicity; it is suspected that elevated chlorine
concentrations were a factor in the facility failing it's whole effluent toxicity test. The NC instream action
level for total residual chlorine is 17 ug/l. If the facility utilizes a method of disinfection other than wastewater
chlorination, this limit would not be necessary, otherwise effluent dechlorination should be a written permit
condition.
The ammonia limit, while being limited for its oxygen consuming characteristic, is also limited as a
toxic substance. The recognition and documentation of ammonia toxicity led to the adoption of Division
procedure protecting the instream summer ammonia concentration to 1.0 mg/1 or less. The ammonia limit
would have to be 1.0 mg/1 whether protection of the DO standard required it or not.
All major dischargers in North Carolina are required to perform whole effluent toxicity tests, the type
of which is determined by the instream waste concentration (IWC) during 7Q10 conditions. At the proposed
4.0 MGD wasteflow, Siler City's IWC is 96.1 %, which requires a quarterly chronic toxicity testing at 96%
using Ceriodaphnia as the test organism.

The results of the modeling analysis are shown graphically in Figure 1, and the
model inputs are listed in Table 1. As can be seen in the predicted DO profiles in Figure
1, very severe impacts are expected to result from the relaxed limits (even though the
EMC criteria are not expected to be violated).
The U.S. EPA Criteria Document for Dissolved Oxygen (1986) states that no
additional anthropogenic (i.e., human generated) sources of oxygen -consuming waste
should be allowed into systems not attaining a one -day minimum concentration of 3.0
mg/I. 3.0 mg/I is the threshold level for warm water fish survival. Technical Support
recommends that the requested flow increase not be approved for the following reasons:
1) The Siler City WWTP is currently under moratorium.
2) Loves Creek and the Rocky River are already severely impacted and regularly
experience substandard DO concentrations that violate EPA minimum
criteria for fish survival under current loading conditions.
3) It seems counterproductive to allow any more wastewater to be accepted by
the plant, unless absolutely necessary, until the effluent and downstream
water quality are improved.
4) The facility's poor compliance record should not be rewarded with additional
flow until definitive action is taken toward improvement.
5) The proposed limits are expected to result in anoxic conditions for a
significant portion of the stream; this should be prevented if at all possible.
Please contact me if further clarification is needed.
cc: Steve Tedder
Kent Wiggins
Central Files